Distribution of Total and DTPA‐Extractable Zinc,Copper, Manganese,and Iron in Vertisols of India

Abstract

Vertisols of India are developed over isohyets of 600 to 1500 mm, and their chemical cycles are set by drainage, landforms, and particle size, which results in variable pedogenic development within the otherwise homogeneous soils. The purpose of this study was to identify pedogenic processes in the distribution of total and DTPA‐extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The soils are developed over basaltic parent material of Cretaceous age. Soil samples were drawn from genetic horizons of the 13 benchmark profiles and analyzed by using HF–HClO₄ acid for total and DTPA extraction. Correlation coefficients were calculated taking all samples together. The total concentration varied from 24 to 102 mg kg^?1 for Zn, 21 to 148 mg kg^?1 for Cu, 387 to 1396 mg kg^?1 for Mn, and 2.36 to 9.50% for Fe. Their variability was proisotropic and haplodized, and their concentrations increased with advancing isohyets. Within the isohyets, hindrance in drainage caused retention of Zn and Cu but loss of Fe. The piedmont soils had more Fe than alluvium soils. The spatial distribution of total contents of Zn, Cu, and Fe was influenced by the pedogenic processes associated with Haplusterts but not with provenance materials. Surface concentrations of the elements by biotic lifting and/or harvest removal were negated by the pedoturbation that further contributed to the irregular distribution of the elements in the profiles. Total Zn and total Cu had positive coefficients of correlations with coarse clay, whereas total Mn and total Fe were positively correlated with fine clay. The DTPA‐extractable forms were functions of isohyets and drainage and showed association with organic carbon content and coarse clay.     

Zinc nutrition and levels of endogenous lndole‐3‐acetic acid in radish shoots

Radish (Raphanus sativus cv. Akamaru‐Hatsukadaikon) was grown for several experiments in a glasshouse with zinc (Zn) supply in the nutrient solution. Lack of Zn resulted in stunted growth and reduced leaf of radish shoots were observed. Two‐dimensional thin layer chromatography (TLC) and gas chromatography‐mass spectrometry (GC‐MS) analysis revealed the presence of endogenous indole‐3‐acetic acid (IAA) in Zn‐deficient radish shoots. An estimate has been made of alkali‐labile (1 and 7N NaOH) IAA in Zn‐deficient radish shoots with the use of gas chromatography (GC). The level of 7N NaOH‐labile IAA (peptidic + ester + free) and IN NaOH‐labile IAA (ester + free) in Zn‐deficient radish shoots was almost the same as that of control radish shoots. These results suggest that Zn nutrition did not affect the level of endogenous IAA in radish shoots.     

Effect of Zinc Humate on Growth of Soybean and Wheat in Zinc‐Deficient Calcareous Soil

Abstract

Humic acids have many benefits for plant growth and development, and these effects may be maximized if these materials are combined with micronutrient applications. In the present study, pot experiments were conducted to evaluate the effects of zinc (Zn) humate and ZnSO₄ on growth of wheat and soybean in a severely Zn‐deficient calcareous soil (DTPA‐Zn: 0.10 mg kg^?1 soil). Plants were grown for 24 (wheat) and 28 days (soybean) with 0 or 5 mg kg^?1 of Zn as either ZnSO₄ or Zn humate. Zinc humate used in the experiments was obtained from Humintech GmbH, Germany, and contained 5% of Zn. When Zn was not supplied, plants rapidly developed visible symptoms of Zn deficiency (e.g., chlorosis and brown patches on young leaves in soybean and necrotic patches on middle‐aged leaves in wheat). Adding Zn humate eliminated Zn‐deficiency symptoms and enhanced dry matter production by 50% in soybean and 120% in wheat. Zinc‐humate and ZnSO₄ were similarly effective in increasing dry matter production in wheat; but Zn humate increased soybean dry matter more than ZnSO₄. When Zn was not supplied, Zn concentrations were 6 mg kg^?1 for wheat and 8 mg kg^?1 for soybean. Application of Zn humate and ZnSO₄ increased shoot Zn concentration of plants to 36 and 34 mg kg^?1 in wheat and to 13 and 18 mg kg^?1 in soybean, respectively. The results indicate that soybean and wheat plants can efficiently utilize Zn chelated to humic acid in calcareous soils, and this utilization is comparable to the utilization of Zn from ZnSO₄. Under Zn‐deficient soil conditions, plant growth and yield can be maximized by the combined positive effects of Zn and humic acids.     

Release Rates of Ammonium‐Nitrogen,Nitrate‐Nitrogen,Phosphorus, Potassium,Magnesium, Iron,and Manganese from Seven Controlled‐Release Fertilizers

Abstract

Samples of seven controlled‐release fertilizers, Nutricote Total 13–13–13, Nutricote Total 18–6–8, Osmocote Plus 15–9–12, Osmocote 13–13–13, Polyon 18–6–12, Polyon 14–14–14, and Plantacote 14–8–15, were placed in leaching columns containing acid‐washed sand. Samples of all leachates were analyzed weekly to determine release rates of ammonium‐nitrogen (N), nitrate‐N, phosphorus (P), potassium (K), magnesium (Mg), manganese (Mn), and iron (Fe). Release rates for P from all products were slower than those for NH₄‐N, NO₃‐N, and K. Release of Mg, Mn, and Fe was very poor, with less than 50% of the total amount of each of these elements ever being released from the prills for some products. Nutricote products released Fe and Mn more effectively than did Osmocote or Plantacote.     

Effect of Zinc × Boron Interaction on Plant Growth and Tissue Nutrient Concentration of Corn

ABSTRACT

A pot experiment was conducted in a greenhouse on a calcareous soil (fine, mixed, mesic, Fluventic Haploxerepts) to study the interaction of zinc (Zn) and boron (B) on the growth and nutrient concentration of corn (Zea mays L.). Treatments consisted of a factorial arrangement of seven levels of B (0, 2.5, 5, 10, 20, 40, and 80 mg kg^{? 1}as boric acid), two sources of Zn [zinc sulfate (ZnSO₄ · 7H₂O) and zinc oxide (ZnO)], and three levels of Zn (0, 5, and 10 mg kg^{? 1}) in a completely randomized design with three replications. Plants were grown for 70 d in 1.6 L plastic containers. Applied Zn significantly increased plant height and dry matter yield (DMY) of corn. Source of Zn did not significantly affect growth or nutrient concentration. High levels of B decreased plant height and DMY. There was a significant B × Zn interaction on plant growth and tissue nutrient concentration which were rate dependent. In general, the effect of B × Zn interaction was antagonistic on nutrient concentration and synergistic on growth. It is recommended that the plants be supplied with adequate Zn when corn is grown in high B soils, especially when availability of Zn is low.     

Fraction Distributions of Lead,Cadmium, Copper,and Zinc in Metal‐Contaminated Soil before and after Extraction with Disodium Ethylenediaminetetraacetic Acid

Abstract: The fraction distributions of heavy metals have attracted more attention because of the relationship between the toxicity and their speciation. Heavy‐metal fraction distributions in soil contaminated with mine tailings (soil A) and in soil irrigated with mine wastewater (soil B), before and after treatment with disodium ethylenediaminetetraacetic acid (EDTA), were analyzed with Tessier's sequential extraction procedures. The total contents of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) exceeded the maximum permissible levels by 5.1, 33.3, 3.1, and 8.0 times in soil A and by 2.6, 12.0, 0.2, and 1.9 times in soil B, respectively. The results showed that both soils had high levels of heavy‐metal pollution. Although the fractions were found in different distribution before extraction, the residual fraction was found to be the predominant fraction of the four heavy metals. There was a small amount of exchangeable fraction of heavy metals in both contaminated soils. Furthermore, in this study, the extraction efficiencies of Pb, Cd, and Cu were higher than those of Zn. After extraction, the concentrations of exchangeable Pb, Cd, Cu, and Zn increased 84.7 mg·kg^?1, 0.3 mg·kg^?1, 4.1 mg·kg^?1, and 39.9 mg·kg^?1 in soil A and 48.7 mg·kg^?1, 0.6 mg·kg^?1, 2.7 mg·kg^?1, and 44.1 mg·kg^?1 in soil B, respectively. The concentrations of carbonate, iron and manganese oxides, organic matter, and residue of heavy metals decreased. This implies that EDTA increased metal mobility and bioavailability and may lead to groundwater contamination.     

Short‐Term Effect of Lime,Phosphorus, and Iron Amendments on Water‐Extractable Lead and Arsenic in Orchard Soils

Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO₃), iron hydroxide [Fe(OH)₃], and potassium phosphate (KH₂PO₄) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H₂PO₄ ^? and dihydrogen arsenate (H₂AsO₄ ^?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.     

Determination of Mugineic Acid, 2′-Deoxymugineic Acid, 3-Hydroxymugineic Acid,and Their Iron Complexes by Ion-Pair HPLC and Colorimetric Procedures

Extract

Under iron (Fe)-deficient conditions like in calcareous and/or high pH soils, mugineic acid family phytosiderophores (MAs: mugineic acid (MA), 2′-deoxymugineic acid (DMA), 3-hydroxymugineic acid (HMA) etc.) are secreted from graminaceous plants and solubilize the slightly soluble Fe in soil as MAs-Fe complexes (Takagi 1976, 1993). Due to their high availability to higher plants (Roemheld and Marschner 1986), the behavior of MAs and their Fe complexes in the soil environment is of interest in connection with the iron nutrition of these plants.     

Effect of Soil Sodicity on Growth,Yield, Essential Oil Composition,and Cation Accumulation in Rose‐Scented Geranium

Abstract

The effect of soil sodicity [exchangeable sodium percentage (ESP)] on the growth, yield, essential oil composition, and cation accumulation of two cultivars (Bourbon and Cimpawan) of geranium (Pelargonium graveolens) were studied in a pot experiment. Irrespective of soil sodicity, two cultivars of geranium differed significantly in their plant height and herb and oil yield. Plant height was not significantly affected with increases in soil ESP from 0.7 (control) to 20.0 and 7.0, respectively, for cultivars (cv) Bourbon and Cimpawan, but further increase in soil ESP decreased the plant height. The herb yield of cv Bourbon significantly increased with increasing soil ESP to 16.0, and the oil yield increased with increasing ESP to 7.0. Further increase in soil ESP decreased the yield. The increase in yield of cv Bourbon was 13.1 and 15.1% in the herb and 40.0 and 15.2% in the oil over the control (ESP 0.7) at soil ESP of 7.0 and 16.0, respectively. Decreases in yield were 3.5, 4.9, 53.3, and 59.3% in the herb yield and 3.8, 5.7, 53.3, and 80.0% in the oil over control (ESP 0.7) at soil ESP of 20.0, 24.0, 28.0, and 30.0, respectively. The herb and oil yield of cv Cimpawan significantly decreased with increase in soil ESP. The decease in yield was 17.7, 20.2, 40.7, 53.1, 70.7, and 72.6% in the herb and 4.0, 6.8, 30.9, 45.4, 83.2, and 84.0% in the oil over control (soil ESP 0.7) at the soil ESP 7.0, 16.0, 20.0, 24.0, 28.0, and 30.0, respectively. The concentration of isomenthone, linalool, citronellyl formate, and geranyl formate in the essential oil increased at low levels of soil ESP (between 16.0 to 24.0) but decreased at high soil ESP (>28). The concentration of l‐citronellol, nerol, and geraniol gradually increased with increase in soil ESP. The increase in the soil ESP enhanced the concentration of sodium (Na) and decreased that of potassium (K) in shoot and root tissues of geranium as compared to control. The concentration of Ca in shoot tissues of cv Bourbon significantly decreased with increase in soil ESP, but in the cv Cimpawan, the Ca concentration was not significantly affected with increase in soil ESP from 0.7 to 16.0, and thereafter the Ca concentration significantly decreased with further increase in soil ESP. The concentration of Na, K, and Ca were relatively higher in shoot than in root tissues. The K/Na and Ca/Na ratios in shoot tissues of both cultivars of geranium decreased with increase in soil ESP. The K/Na and Ca/Na ratios in shoot were not found to be related to the differences in sodicity tolerance of the cultivars of geranium tested in this experiment. The concentration of zinc (Zn) in shoot tissues decreased with increase in soil ESP. The cv Bourbon maintained a higher concentration of Zn in shoot tissues at high sodicity than that of cv Cimpawan. The results suggest that the geranium is slightly to moderately tolerant of soil sodicity stress.     

Influence of Integrated Supply of Vermicompost and Zinc‐Eniched Compost with Two Graded Levels of Iron and Zinc on the Productivity of Geranium

Abstract

Two pot experiments under greenhouse condition were carried out to study the influence of vermicompost and zinc‐enriched compost with two levels of iron and zinc on the productivity of geranium (Pelargonium graveolens). Joint application of vermicompost and zinc‐enriched compost was effective in increasing the herb and oil yield over sole application of iron and zinc. Combined application of vermicompost and zinc‐enriched compost gave better herb and oil yield in both the experiments. With application of vermicompost and zinc‐enriched compost with two graded levels of iron, higher N, P, and K concentrations were observed with application of vermicompost (5 g kg^?1), vermicompost (5 g kg^?1), and Fe 12.5 ppm+Zn‐enriched compost 2.5 g kg^?1 soil, respectively, over control. Highest reduction in soil pH was observed with an application of vermicompost at 5 g kg^?1 soil; maximum soil organic carbon content was also recorded in the same treatment. In experiment II, joint application of vermicompost, zinc‐enriched compost, and graded levels of zinc recorded highest N, P, and K concentration with treatments of Zn (15 ppm)+vermicompost (2.5 g kg^?1), vermicompost (5 g kg^?1), and Zn (15 ppm)+vermicompost (2.5 g kg^?1 soil), respectively. Nitrogen, P, and K content increased by 36, 125, and 305%, respectively, with these treatments over the control.

Chemical constituents of geranium oil such as cis‐rose oxide, isomenthone, linalool, citronellyl, geranylformate, geranyl, and epi‐γ‐eudesmol were significantly improved by combined application of Zn with vermicompost and Zn‐enriched compost as compared to sole application of Zn. Similar effects were observed with Fe in combination with vermicompost and Zn‐enriched compost on most of the chemical constituents of geranium oil. Physicochemical properties of the soil were also improved as macro‐ and micronutrient availability markedly increased in both the experiments because of combined application of vermicompost and Zn‐enriched compost with two levels of Zn and Fe.     

Time of Day Effect on Foliar Nutrient Concentrations in Corn and Soybean

Foliar nutrient concentrations vary during the day. Field research was conducted to quantify and better understand this variation in corn (Zea mays L.) and soybean (Glycine max L. Merr.) with foliar sampling during the vegetative and reproductive stages. Time of day effects occurred inconsistently across nutrients. Nitrogen (N), manganese (Mn), iron (Fe), and zinc (Zn) foliar concentrations were generally high early in the day. Phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) foliar concentrations varied inconsistently with time of day, while concentrations of boron (B) in both crops and copper (Cu) in corn were not affected. Limiting foliar sampling to after 10:00 AM reduced the variation for soybean but not for corn. Interpretation by Diagnosis and Recommendation Integrated System (DRIS) did not reduce the time of day effect. The variation caused by time of day, along with other causes, affects confidence in interpretation of foliar results suggesting use of the information with either additional foliar sampling or soil testing in making nutrient management decisions.     

Effect of Grinding on Soil Extraction by Aqua Regia, 2 M Nitric Acid,and Mehlich 3

Abstract

The effect of grinding on soil extraction was determined for two soil fractions and three extractants. Arsenic (As), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) were extracted by aqua regia and 2 M nitric acid. Mehlich 3 extractant was used for determination of potassium (K), magnesium (Mg), calcium (Ca), phosphorus (P), iron (Fe), and aluminum (Al). One hundred forty‐seven agricultural soil samples representing all major soil types, climatic regions, and proportions of agronomic cultures in the Czech Republic were collected for the study. Particle size fractions smaller than 2 mm and smaller than 0.150 mm were chosen for investigation. Extraction of elements by aqua regia was similar for both size fractions of soil. Cold 2 M nitric acid is a weaker extractant than aqua regia, and a statistically significant increase in extractable Be (5%), Cd (6%), Co (11%), Cu (5%), Ni (5%), and V (2%) was measured with the finely ground soils. An increase for the finer fraction for K (10%) and Mn (25%) was found for Mehlich 3. A more complex nonlinear relationship was found for Mehlich 3 extractable Al and Fe. This was probably caused by a more intensive re‐adsorption of Fe and Al to the finely ground soils.     

Effect of Olive‐Derived Organic Amendments on Lead,Zinc, and Biochemical Parameters of an Artificially Contaminated Soil

Abstract

An incubation experiment was conducted to ascertain the effects of three olive‐derived organic amendments (fresh, compost, and vermicompost olive cake) on the soluble and diethylenetriamine pentaacetic acid (DTPA)–extractable lead (Pb) and zinc (Zn) and on different enzymatic activities in an artificially contaminated calcareous soil. Application of the compost and vermicompost, which increased amounts of humic acids in soil, initially stimulated dehydrogenase, ß‐glucosidase, and urease activities, which tended to decline afterward. In contrast, dehydrogenase and ß‐glucosidase activities were lower after application of the fresh olive cake. Amounts of soluble Pb and Zn increased when fresh olive cake was added to the soil, due to the high content of water‐soluble carbon in this amendment. On the contrary, application of the compost and vermicompost decreased the concentration of soluble Zn and did not change the soluble Pb levels in the soil. The DTPA‐Pb and DTPA‐Zn were scarcely affected by the application of the three olive‐derived amendments.     

Effect of Submergence on Iron Transformation and Phosphorus Availability in Calcareous Soils

A thermostatic incubation experiment was carried out to estimate the effects of flooding periods,stalk application and P addition of Fe transformation and P availability in calcareous soils.Submergence increased amorphous Fe,especially in the case of stalk application.The newly formed amorphous Fe with a great surface area played an important role in Psorption;and submergence also stimulated the dissolution of inorganic P,thus increasing the availability of soil P in calcareous soils.Meanwhile,a part of soluble P was absorbed and fixed again on the surface of newly formed amorphous Fe,thus resulting in a decrease of P availability.Soil rapidly available P increased after 150-day incubation.There existed significantly negative correlations between soil amorphous Fe content and soil Fe-P and rapidly available P contents.Submerged conditions promoted the transformation of inorganic P added toward Fe-P in calcareous soils,especially in the case of stalk application.     

Accumulation,partitioning, and assimilation of nitrate in Opuntia ficus‐indica

Nitrate levels and nitrate reductase activity (NRA) of the widely cultivated prickly‐pear Opuntia ficus‐indica were measured for 5‐year‐old orchard plants in the field between flowering and fruit ripening (May‐August) and for rooted cladodes (stem segments) in a glasshouse in pots that were supplied with 0.8,4, or 16 mM nitrate during the early growth of new cladodes (6 weeks). Nitrate levels were much higher in the cladodes than in the fruit peels or the roots; in both cladodes and fruit peels, nitrate levels were higher in the inner water‐storing layer (parenchyma) than in the outer green photosynthetic layer (chlorenchyma). NRA was confined to the cladode chlorenchyma and was higher in new cladodes than in the underlying cladodes. The orchard study suggested that the nitrate accumulated in 2‐ and 3‐year‐old cladodes served as a reserve for the growth of new organs. At the beginning of the reproductive season, such older cladodes had high nitrate levels of 7 mg/g DW in the chlorenchyma and 45 mg/g DW in the parenchyma, which decreased by 72% and 43%, respectively, by the end of the season. The glasshouse experiments indicated that the cladodes were more important for nitrate reduction than the roots, particularly under high external nitrate concentrations.     

Adsorption of Copper,Zinc, and Cadmium on Goethite,Aluminum‐Substituted Goethite,and a System of Kaolinite–Goethite: Surface Complexation Modeling

Abstract

Goethite, aluminum‐(Al)‐substituted goethite (GA2), and a system of kaolinite–goethite were examined for their ability to adsorb copper (Cu), zinc (Zn), and cadmium (Cd) as a function of pH, in two ionic strengths and two different metal concentrations. Specific surface area was determined by BET‐N₂, whereas the charge development on the solid surface was studied in the pH range ～3.5 to ～10.0 by potentiometric titration under continuous flow of argon.

Constant capacitance (CCM) and the double‐layer model (DLM) were used to fit the titration and adsorption data with the help of the least‐square optimization program FITEQL32. In both models, surface site density was fixed at Ns=2.31 sites nm^?2, whereas for CCM capacitance density was set at C=1.06. Alternatively, bibliographic suggestions for these two parameters were examined.

Aluminum‐substituted goethite exhibited higher specific surface area and adsorbed all three metals in lower pH values than the other solids. Moreover, GA2 exhibited point of zero salt effect (PZSE) higher than goethite, approaching that corresponding to Al₂O₃, possibly due to Al‐substitution, and the system exhibited PZSE values much higher than kaolinite, approaching that corresponding to goethite. The adsorption order for all three solids was Cu>Zn>Cd in any case, thus more Cu is adsorbed at a certain pH than Zn and even more than Cd, whereas the increase of metal concentration shifts the adsorption curve toward higher pH values.

Constant capacitance described the titration data satisfactorily, but by altering the Ns and C values, the fit became worse. Adsorption data are described by CCM, by emphasizing the formation of monodentate surface complex. Bidentate complex, in most of the cases, was of no importance in describing the data despite the evidence of its presence in recent spectroscopic studies for Cu and Cd on goethite. Alteration of Ns and C values worsened the fit in any case, and bidentate complex vanished. The DLM exhibited the worse fit in any case.     

Distribution and Accumulation of Copper and Cadmium in Soil–Rice System as Affected by Soil Amendments

The effects of seven amendments on the distribution and accumulation of copper and cadmium in a soil–rice system were investigated using a pot experiment. Results showed that application of limestone, calcium magnesium phosphate (Ca–Mg–P fertilizer), calcium silicate (silicon fertilizer), Chinese milk vetch, pig manure, and peat significantly decreased the concentrations of Cu and Cd in rice roots by 24.8–75.3% and 9.7–49.9%, respectively. However, no significant difference was observed between zinc sulfate (zinc fertilizer) and the control treatment. The concentrations of Cu and Cd in different parts of rice followed the order: root > straw > grain, and all amendments restrained the transfer of Cu and Cd from rice root to stem. Copper and Cd concentrations in rice stems at the tillering stage were the highest, and then decreased from the tillering stage to the heading stage. However, they increased again at the ripening stage. The results also showed that application of amendments changed Cu and Cd solubility in soil and decreased their bioavailability, which resulted in the reduction of Cu and Cd uptake by rice. Significant correlations between the concentrations of Cu and Cd in soil solutions and in rice stems were found. The result demonstrated that limestone has the best efficiency among all the amendments used in reducing Cu and Cd contamination to rice production.     

Effect of Low‐Rate Commercial Humic Acid on Phosphorus Availability,Micronutrient Uptake,and Spring Wheat Yield

Abstract

A greenhouse study was conducted to determine the effects of low‐rate commercial humic acid (HA) on phosphorus (P), iron (Fe), and zinc (Zn) availability and spring wheat yields, in both a calcareous soil and a noncalcareous soil. In Phase I, soluble P concentrations were monitored at 1.9, 3.8, and 5.7 cm from a monoammonium phosphate (MAP) fertilizer band that had either been coated with one of two HA products at the equivalent of 1.7 kg HA ha^?1, a label rate, or left uncoated. Sampling occurred periodically up to 48 d after fertilizer application. In Phase II, uptake of P, Fe, and Zn and grain yield were measured in soils that had been fertilized with 7.5 or 25 kg P ha^?1, either coated with HA or left uncoated. In Phase I, only three significant differences (P=0.05) out of 66 comparisons were found in soluble P concentrations between HA and control treatments at time points ranging from 4 to 48 d after fertilization. In addition, no significant differences were found in nutrient uptake, shoot biomass, or grain yield between HA and control treatments. These greenhouse results suggest that low commercial HA rates (～1.7 kg HA ha^?1) may be insufficient to enhance spring wheat growth.     

Effect of B,Mn and Zn on nodulation and N2‐fixation in southernpeas

Abstract

Two greenhouse studies were conducted to evaluate the effect of B, Mn and Zn on nodulation and N₂‐fixation of southernpea (Vigna unguiculata (L.) Halp.) cultivars ‘Freezegreen’, ‘Mississippi Silver’ and ‘Pinkeye Purple Hull’. The cultivars were grown in plastic pots with a Norfolk sandy loam (fine, loamy siliceous thermic, Typic Paleudult) soil treated with B, Mn and Zn at rates of 0, 5, 10 and 20 kg/ha each at pH levels 5.5, 6.0 and 6.5. At pH 6.5 all micronutrient treatments significantly increased nodulation and N₂‐fixation over the control (no micronutrient applied). The effects of B, Mn and Zn on nodulation and N₂‐fixation depended on the cultivar and soil pH. For plants given the 5 kg/ha B and Mn treatments, ‘Mississippi Silver’ produced the highest number of nodules and ‘Pinkeye Purple Hull’ the least. At 20 kg/ha Zn, nodulation of ‘Freezegreen’ was highest and ‘Pinkeye Purple Hull’ the lowest. As a whole, maximum nodulation was at 5 kg/ha B and Mn and 20 kg/ha for Zn. Nitrogen fixation rates responded similarly except that the optimum rate for Zn was 10 kg/ha. Seed yield of plants peaked at 5 kg/ha for B and 10 kg/ha for Zn, indicating a possible relation of N₂‐fixation to seed yield.     

Zinc adsorption by sterilized and non‐sterilized soil in the presence of citrate and catechol

Abstract

The effect of organic ligands on zinc (Zn) adsorption in the rhizosphere may be influenced by microbial activity depleting the concentration of the ligand over time. Zinc adsorption by sterile and non‐sterile lateritic soil was measured by shaking the soils with Zn solutions at a soil‐liquid ratio of 1: 5 for five periods of time ranging from 17–480 h. The concentrations of Zn and the ligands were determined after the selected times. The speciation of Zn was then estimated.

Changes in Zn adsorption with time in the presence of organic ligands were due to changes in pH and Zn complexation associated with the addition and breakdown of the organic ligands and with the technique of sterilization. Zinc adsorption was higher in non‐sterile than in sterile soil. Adsorption in the presence of citrate was lower than in its absence except in non‐sterile soil after 72 h. The adsorption in the presence of catechol was similar to that in its absence.